/*
 * Copyright (C) 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.nativescript.widgets.image;

import android.Manifest;
import android.annotation.TargetApi;
import android.content.Context;
import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.BitmapFactory;
import android.os.Build.VERSION_CODES;
import android.os.Environment;
import android.os.StatFs;
import android.util.Log;
import android.util.LruCache;

import java.io.File;
import java.lang.ref.SoftReference;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

/**
 * This class handles disk and memory caching of bitmaps in conjunction with the
 * {@link Worker} class and its subclasses. Use
 * {@link Cache#getInstance(CacheParams)} to get an instance of this
 * class, although usually a cache should be added directly to an {@link Worker} by calling
 * {@link Worker#addImageCache(Cache)}.
 */
public class Cache {
	private static final String TAG = "JS";

	// Default memory cache size in kilobytes
	private static final int DEFAULT_MEM_CACHE_SIZE = 1024 * 5; // 5MB

	// Constants to easily toggle various caches
	private static final boolean DEFAULT_MEM_CACHE_ENABLED = true;
	private static final boolean DEFAULT_DISK_CACHE_ENABLED = true;

	private static Cache instance;
	private HashMap<String, Integer> mMemoryCacheUsage;
	private LruCache<String, Bitmap> mMemoryCache;
	private CacheParams mParams;

	private Set<SoftReference<Bitmap>> mReusableBitmaps;

	/**
	 * Create a new Cache object using the specified parameters. This should not be
	 * called directly by other classes, instead use
	 * {@link Cache#getInstance(CacheParams)} to fetch an Cache
	 * instance.
	 */
	private Cache() {
	}

	/**
	 * Return an {@link Cache} instance.
	 *
	 * @return An existing retained Cache object or a new one if one did not exist
	 */
	public static Cache getInstance(CacheParams cacheParams) {
		if (instance == null) {
			instance = new Cache();
		}

		if (instance.mParams != cacheParams) {
			instance.init(cacheParams);
		}

		return instance;
	}

	/**
	 * Initialize the cache, providing all parameters.
	 *
	 * @param cacheParams The cache parameters to initialize the cache
	 */
	private void init(CacheParams cacheParams) {
		clearCache();
		if (mReusableBitmaps != null) {
			mReusableBitmaps.clear();
			mReusableBitmaps = null;
		}

		mParams = cacheParams;

		// Set up memory cache
		if (mParams.memoryCacheEnabled) {
			if (Worker.debuggable > 0) {
				Log.v(TAG, "Memory cache created (size = " + mParams.memCacheSize + ")");
			}

			// If we're running on Honeycomb or newer, create a set of reusable bitmaps that can be
			// populated into the inBitmap field of BitmapFactory.Options. Note that the set is
			// of SoftReferences which will actually not be very effective due to the garbage
			// collector being aggressive clearing Soft/WeakReferences. A better approach
			// would be to use a strongly references bitmaps, however this would require some
			// balancing of memory usage between this set and the bitmap LruCache. It would also
			// require knowledge of the expected size of the bitmaps. From Honeycomb to JellyBean
			// the size would need to be precise, from KitKat onward the size would just need to
			// be the upper bound (due to changes in how inBitmap can re-use bitmaps).
			if (Utils.hasHoneycomb()) {
				mReusableBitmaps =
					Collections.synchronizedSet(new HashSet<SoftReference<Bitmap>>());
			}

			mMemoryCacheUsage = new HashMap<String, Integer>();
			mMemoryCache = new LruCache<String, Bitmap>(mParams.memCacheSize) {

				/**
				 * Notify the removed entry that is no longer being cached
				 */
				@Override
				protected void entryRemoved(boolean evicted, String key,
																		Bitmap oldValue, Bitmap newValue) {
					Integer count = mMemoryCacheUsage.get(key);
					if (Utils.hasHoneycomb() && (count == null || count == 0)) {
						// We're running on Honeycomb or later, so add the bitmap
						// to a SoftReference set for possible use with inBitmap later
						mReusableBitmaps.add(new SoftReference<Bitmap>(oldValue));
					}
				}

				/**
				 * Measure item size in kilobytes rather than units which is more practical
				 * for a bitmap cache
				 */
				@Override
				protected int sizeOf(String key, Bitmap value) {
					final int bitmapSize = getBitmapSize(value) / 1024;
					return bitmapSize == 0 ? 1 : bitmapSize;
				}
			};
		}
	}

	/**
	 * Adds a bitmap to both memory and disk cache.
	 *
	 * @param data  Unique identifier for the bitmap to store
	 * @param value The bitmap drawable to store
	 */
	public void addBitmapToCache(String data, Bitmap value) {
		if (data == null || value == null) {
			return;
		}

		// Add to memory cache
		if (mMemoryCache != null) {
			Bitmap currentValue = mMemoryCache.get(data);
			// NOTE: If we have existing we probably loaded it sync so we don't want to add the new one,
			// because this will make the previous bitmap free for reuse but it is used somewhere.
			// Probably won't happen often.
			if (currentValue == null) {
				Integer count = mMemoryCacheUsage.get(data);
				// NOTE: count should be null here.
				mMemoryCacheUsage.put(data, count == null ? 1 : count + 1);
				mMemoryCache.put(data, value);
			}
		}
	}

	/**
	 * Get from memory cache.
	 *
	 * @param data Unique identifier for which item to get
	 * @return The bitmap if found in cache, null otherwise
	 */
	public Bitmap getBitmapFromMemCache(String data) {
		Bitmap memValue = null;

		if (mMemoryCache != null) {
			memValue = mMemoryCache.get(data);
			if (memValue != null) {
				Integer count = mMemoryCacheUsage.get(data);
				mMemoryCacheUsage.put(data, count == null ? 1 : count + 1);
			}
		}

		if (Worker.debuggable > 0 && memValue != null) {
			Log.v(TAG, "Memory cache hit");
		}

		return memValue;
	}

	public void reduceDisplayedCounter(String uri) {
		if (mMemoryCache != null) {
			Integer count = mMemoryCacheUsage.get(uri);
			if (count != null) {
				if (count == 1) {
					mMemoryCacheUsage.remove(uri);
				} else {
					mMemoryCacheUsage.put(uri, count - 1);
				}
			}
		}
	}

	/**
	 * @param options - BitmapFactory.Options with out* options populated
	 * @return Bitmap that case be used for inBitmap
	 */
	protected Bitmap getBitmapFromReusableSet(BitmapFactory.Options options) {
		//BEGIN_INCLUDE(get_bitmap_from_reusable_set)
		Bitmap bitmap = null;

		if (mReusableBitmaps != null && !mReusableBitmaps.isEmpty()) {
			synchronized (mReusableBitmaps) {
				final Iterator<SoftReference<Bitmap>> iterator = mReusableBitmaps.iterator();
				Bitmap item;

				while (iterator.hasNext()) {
					item = iterator.next().get();

					if (null != item && item.isMutable()) {
						// Check to see it the item can be used for inBitmap
						if (canUseForInBitmap(item, options)) {
							bitmap = item;

							// Remove from reusable set so it can't be used again
							iterator.remove();
							break;
						}
					} else {
						// Remove from the set if the reference has been cleared.
						iterator.remove();
					}
				}
			}
		}

		return bitmap;
		//END_INCLUDE(get_bitmap_from_reusable_set)
	}

	/**
	 * Clears both the memory and disk cache associated with this Cache object. Note that
	 * this includes disk access so this should not be executed on the main/UI thread.
	 */
	public void clearCache() {
		if (mMemoryCache != null) {
			mMemoryCache.evictAll();
			if (Worker.debuggable > 0) {
				Log.v(TAG, "Memory cache cleared");
			}
		}
		if (mMemoryCacheUsage != null) {
			mMemoryCacheUsage.clear();
		}

		mMemoryCacheUsage = null;
		mMemoryCache = null;
	}

	/**
	 * A holder class that contains cache parameters.
	 */
	public static class CacheParams {
		public int memCacheSize = DEFAULT_MEM_CACHE_SIZE;
		public boolean memoryCacheEnabled = DEFAULT_MEM_CACHE_ENABLED;
		public boolean diskCacheEnabled = DEFAULT_DISK_CACHE_ENABLED;

		/**
		 * Sets the memory cache size based on a percentage of the max available VM memory.
		 * Eg. setting percent to 0.2 would set the memory cache to one fifth of the available
		 * memory. Throws {@link IllegalArgumentException} if percent is < 0.01 or > .8.
		 * memCacheSize is stored in kilobytes instead of bytes as this will eventually be passed
		 * to construct a LruCache which takes an int in its constructor.
		 * <p>
		 * This value should be chosen carefully based on a number of factors
		 * Refer to the corresponding Android Training class for more discussion:
		 * http://developer.android.com/training/displaying-bitmaps/
		 *
		 * @param percent Percent of available app memory to use to size memory cache
		 */
		public void setMemCacheSizePercent(float percent) {
			if (percent < 0.01f || percent > 0.8f) {
				throw new IllegalArgumentException("setMemCacheSizePercent - percent must be "
					+ "between 0.01 and 0.8 (inclusive)");
			}
			memCacheSize = Math.round(percent * Runtime.getRuntime().maxMemory() / 1024);
		}
	}

	/**
	 * @param candidate     - Bitmap to check
	 * @param targetOptions - Options that have the out* value populated
	 * @return true if <code>candidate</code> can be used for inBitmap re-use with
	 * <code>targetOptions</code>
	 */
	@TargetApi(VERSION_CODES.KITKAT)
	private static boolean canUseForInBitmap(
		Bitmap candidate, BitmapFactory.Options targetOptions) {
		//BEGIN_INCLUDE(can_use_for_inbitmap)
		if (!Utils.hasKitKat()) {
			// On earlier versions, the dimensions must match exactly and the inSampleSize must be 1
			return candidate.getWidth() == targetOptions.outWidth
				&& candidate.getHeight() == targetOptions.outHeight
				&& targetOptions.inSampleSize == 1;
		}

		// From Android 4.4 (KitKat) onward we can re-use if the byte size of the new bitmap
		// is smaller than the reusable bitmap candidate allocation byte count.
		int width = targetOptions.outWidth / targetOptions.inSampleSize;
		int height = targetOptions.outHeight / targetOptions.inSampleSize;
		int byteCount = width * height * getBytesPerPixel(candidate.getConfig());
		return byteCount <= candidate.getAllocationByteCount();
		//END_INCLUDE(can_use_for_inbitmap)
	}

	/**
	 * Return the byte usage per pixel of a bitmap based on its configuration.
	 *
	 * @param config The bitmap configuration.
	 * @return The byte usage per pixel.
	 */
	private static int getBytesPerPixel(Config config) {
		if (config == Config.ARGB_8888) {
			return 4;
		} else if (config == Config.RGB_565) {
			return 2;
		} else if (config == Config.ARGB_4444) {
			return 2;
		} else if (config == Config.ALPHA_8) {
			return 1;
		}
		return 1;
	}

	/**
	 * Get a usable cache directory (external if available, internal otherwise).
	 *
	 * @param context    The context to use
	 * @param uniqueName A unique directory name to append to the cache dir
	 * @return The cache dir
	 */
	public static File getDiskCacheDir(Context context, String uniqueName) {
		// Check if media is mounted or storage is built-in, if so, try and use external cache dir
		// otherwise use internal cache dir
		final File cacheFilePath = Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) ||
			!isExternalStorageRemovable() ? getExternalCacheDir(context) : context.getCacheDir();
		// In case there is no external storage isExternalStorageRemovable returns False and we get Null from getExternalCacheDir.
		// If this is the case - fall back to internal cache dir.
		final String cachePath = cacheFilePath != null ? cacheFilePath.getPath() : context.getCacheDir().getPath();
		return new File(cachePath + File.separator + uniqueName);
	}

	/**
	 * A hashing method that changes a string (like a URL) into a hash suitable for using as a
	 * disk filename.
	 */
	public static String hashKeyForDisk(String key) {
		String cacheKey;
		try {
			final MessageDigest mDigest = MessageDigest.getInstance("MD5");
			mDigest.update(key.getBytes());
			cacheKey = bytesToHexString(mDigest.digest());
		} catch (NoSuchAlgorithmException e) {
			cacheKey = String.valueOf(key.hashCode());
		}
		return cacheKey;
	}

	private static String bytesToHexString(byte[] bytes) {
		// http://stackoverflow.com/questions/332079
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < bytes.length; i++) {
			String hex = Integer.toHexString(0xFF & bytes[i]);
			if (hex.length() == 1) {
				sb.append('0');
			}
			sb.append(hex);
		}
		return sb.toString();
	}

	/**
	 * Get the size in bytes of a bitmap in a BitmapDrawable. Note that from Android 4.4 (KitKat)
	 * onward this returns the allocated memory size of the bitmap which can be larger than the
	 * actual bitmap data byte count (in the case it was re-used).
	 *
	 * @param bitmap
	 * @return size in bytes
	 */
	@TargetApi(VERSION_CODES.KITKAT)
	public static int getBitmapSize(Bitmap bitmap) {
		// From KitKat onward use getAllocationByteCount() as allocated bytes can potentially be
		// larger than bitmap byte count.
		if (Utils.hasKitKat()) {
			return bitmap.getAllocationByteCount();
		}

		if (Utils.hasHoneycombMR1()) {
			return bitmap.getByteCount();
		}

		// Pre HC-MR1
		return bitmap.getRowBytes() * bitmap.getHeight();
	}

	/**
	 * Check if external storage is built-in or removable.
	 *
	 * @return True if external storage is removable (like an SD card), false
	 * otherwise.
	 */
	@TargetApi(VERSION_CODES.GINGERBREAD)
	public static boolean isExternalStorageRemovable() {
		if (Utils.hasGingerbread()) {
			return Environment.isExternalStorageRemovable();
		}
		return true;
	}

	/**
	 * Get the external app cache directory.
	 *
	 * @param context The context to use
	 * @return The external cache dir
	 */
	@TargetApi(VERSION_CODES.FROYO)
	public static File getExternalCacheDir(Context context) {
		if (Utils.hasFroyo()) {
			if (Utils.hasKitKat() ||
				context.checkPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE, android.os.Process.myPid(), android.os.Process.myUid()) == PackageManager.PERMISSION_GRANTED) {
				return context.getExternalCacheDir();
			}

			return null;
		}

		// Before Froyo we need to construct the external cache dir ourselves
		final String cacheDir = "/Android/data/" + context.getPackageName() + "/cache/";
		return new File(Environment.getExternalStorageDirectory().getPath() + cacheDir);
	}

	/**
	 * Check how much usable space is available at a given path.
	 *
	 * @param path The path to check
	 * @return The space available in bytes
	 */
	@TargetApi(VERSION_CODES.GINGERBREAD)
	public static long getUsableSpace(File path) {
		if (Utils.hasGingerbread()) {
			return path.getUsableSpace();
		}
		final StatFs stats = new StatFs(path.getPath());
		return (long) stats.getBlockSize() * (long) stats.getAvailableBlocks();
	}
}
